It is well established that sand is spread on road surfaces in winter conditions to improve traction where traction might be reduced by the presence of snow and ice.
In some cases salt alone is spread on the road surface in order to melt sheet ice. However the damaging effects of salt are well known in that the chloride ions generate significant levels of corrosion in the concrete and the materials of the roadway and in the vehicles passing over the roadway. In addition the dumping of salt from the roadway into the drains and sewers can cause the salt to enter waterways with further damaging effects to the environment. It is well known therefore that the use of salt is to be avoided wherever possible.
In freezing conditions, moist or wet sand freezes into a solid block so that it is no longer fluid and possible to spread across the roadway. In such freezing conditions, therefore, generally the sand has mixed with it a certain level of salt which is sufficient to prevent the moisture in the sand from freezing so that the sand remains moist but free to be spread. It is also known that dry sand containing little or no moisture remains fluid even when frozen since there is no moisture to solidify and bind the sand particles.
It is well known therefore that if the sand prepared to be spread upon the roadway can be dried, it will remain fluid even in the coldest conditions thus avoiding the necessity for the addition of salt.
Attempts have been made therefore to dry the sand using various techniques generally requiring the application of heat. Asphalt plants can be used for the application of the necessary level of heat to dry the sand but this requires a cost of the heat which is sufficiently high so that the process is not economically viable. It will be appreciated that the winter requirements of a city having a population of the order of 500,000 is of the order of 150,000 tons of sand for the city streets so that the costs of drying the quantity of sand in this amount would be very significant.
Up till now, therefore, there has no viable technique for drying the sand to thus avoid the necessity for the addition of salt.